NCB300 Gas Condensing Combi Boiler for Installers
The NCB300 combi boiler offers the same powerful heating and flexible installation options as larger models, but in a compact design. This combination of features makes the NCB300 gas boiler an excellent choice for smaller properties where reliability and DHW performance are the priority.
- ErP A+ energy efficiency rating*
- Smartphone compatible offering remote adjustments of heating and hot water systems
- Smart weather forecasting and Geofencing
- Durable stainless steel heat exchangers
- 20% Hydrogen-ready
- 5-year parts and labour warranty
- IPX4 rating provides protection from any water leaks
- Extended venting up to 8m
* An A+ energy rating is achieved when installed with 3 Smart Plus room thermostats.
Technical Data
| NCB300-28K | NCB300-37K | NCB300-41K | ||
| Shower rating | Number of showers | One shower | Two showers | Two showers & one tap |
| Heat Output | Heat input range | 24.7/4.3 | 26.8/4.6 | 26.8/4.6 |
| Modulation (max/min) | 6:1 | 6:1 | 6:1 | |
| Heat output range @ 80/60°C | 24.0/4.2kW | 26.0/4.5kW | 26.0/4.5kW | |
| DHW | DHW heat input range | 28.0/4.3kW | 37.0/4.6kW | 41.0/4.6kW |
| DHW output range | 28.0/4.3kW | 37.0/4.6kW | 41.0/4.6kW | |
| DHW flow rate @ 25°C temp. rise. | 16.0 l/min | 21.3 l/min | 23.6 l/min | |
| DHW flow rate @ 35°C temp. rise. | 11.5 l/min | 15.2 l/min | 16.8 l/min | |
| DHW flow rate for kitchen @ 45°C temp. rise. | 9.0 l/min | 11.8 l/min | 13.1 l/min | |
| Modulation | TDR | 7:1 | 8:1 | 9:1 |
| Flue | Flue Size | Coaxial length Ø 60/100 | ||
| Max. horizontal coaxial length Ø60/100 | 8m | |||
| Max. vertical coaxial length Ø60/100 | 8m | |||
| Weight | Lift weight | 29kg | 33kg | 33kg |
| Dimensions | Width x Depth x Height | 395 x 285 x 680mm | ||
| ErP Efficiency | ErP A (93%) | |||
| ErP Efficiency with Smart Plus (x3) | ErP A+ (98%) | |||
| NOx Classification | Class 6 | |||
Navien NCB300 Gase Condensing Boiler FAQs
What does the fault code E302 mean for the NCB300?
E302 This means that the system pressure is too low and you may see that the system pressure gauge indicates that the pressure in the system is below the 1 bar pressure. To re-pressurise the system you will find a filling loop (copper ‘U’ shaped tube with two nuts at each end) on the underside of the boiler or a metal braided flexible hose external of the boiler on the pipework with one or two tap connections at either end of the filling loop.
The tap or taps should be opened a quarter of a turn and the water will start to refill the system (water should be heard filling the system). You should see the pressure gauge rise back up between 1 bar and 1.7 bar pressure and then stop filling. Boiler information on water pressure can also be seen on the digital display by pressing the Eco button for 6 seconds and then scroll through to ‘A6’ which will display the water pressure.
Once the pressure gauge between 1 bar and 1.7 bar turn the taps back to the off position and the water will stop filling the system. The error code 118 will stop and the boiler will now operate. If the error code 118 is still active, fill up the system a little more but not over 2.0 bar. (If you do fill the system too much and the pressure gauge is too high, just bleed water from a radiator until the pressure on the gauge goes down to below 1.7 bar).
To re-pressurise the system you will find a filling loop (metal braided flexible hose) on the underside of the boiler with two tap connections at either end of the filling loop. One small blue & one small black tap handles.
The taps should be opened a quarter of a turn. Open the small black one and then open slowly the small blue one. The water will start to refill the system (water should be heard filling the system). You should see the pressure gauge rise back up between 1 bar and 1.2 bar pressure and then stop filling.
Once the pressure gauge is between 1 bar and 1.2 bar turn the taps back to the off position and the water will stop filling the system. The error code E302 will stop and the boiler will now operate. If the error code E302 is still active, fill up the system a little more but not over 1.5 bar.
(If you do fill the system too much and the pressure gauge is too high, just bleed water from a radiator until the pressure on the gauge goes down to below 1.2 bar).
